The purpose of the study is to determine the prevalence of Hereditary Resistance to Activated Protein C (HRtAPC) in a group of patients with congenital heart disease who have suffered cerebral infarcts. The pilot data will be compared to the known prevalence of the genetic defect in the general population. Based on the results, it will be ascertained whether a prospective trial which investigates whether screening patients with congenital heart disease for the defect and altering treatment for those patients with HRtAPC to prevent strokes is warranted.